Monolithic x-ray image detector and method of manufacturing

Abstract

An x-ray imaging detector comprised of read-out electronics and PIN diodes formed on a high resistivity silicon-on-insulator substrate that permits cell pitches as small as 20 microns. The read-out electronics are fabricated in the thin, top silicon layer of the SOI substrate. The read-out electronics produced provide circuits such as integrators and transimpedance amplifiers which are required to transform the electrical current from PIN diode detectors into an analog voltage. The anodes of the PIN sensor diodes are formed by etching through an oxide barrier layer in the substrate and implanting a heavily doped p+ region into a high resistivity intrinsic silicon layer. X-ray imaging detectors produced by the methods disclosed herein can be assembled into multi-chip modules that can be used in a large panel x-ray imaging apparatus. With a suitable printed circuit board and an edge connector, these panels, using the x-ray image detectors of the present invention, can provide a form, fit and function replacement of film cassettes in existing x-ray equipment.

What is claimed is: 
     
       1. An x-ray imaging detector comprising; a high resistivity substrate;   a plurality of PIN diodes formed in said substrate;   electronic read-out means formed on said substrate in which said PIN diodes have been fabricated to transform the charge collected by each PIN diode into an analog voltage;   whereby said x-ray imaging detector can be connected directly to processing electronics.   
     
     
       2. The detector according to claim 1 in which said PIN diodes comprise; at least one n+ cathode formed on a surface of said high resistivity substrate; and a plurality of heavily doped p+ implanted regions in said substrate forming anodes associated with said n+ cathode. 
     
     
       3. The detector according to claim 2 in which said substrate includes an oxide layer; said p+ implants being implanted in apertures etched through said oxide layer in said substrate. 
     
     
       4. The detector according to claim 3 in which said electronic read-out means comprises a thin silicided poly conductor formed on top of said substrate connected to the anode implant of each of said PIN diodes. 
     
     
       5. The detector according to claim 4 in which said high resistivity substrate comprises a high resistivity epitaxial silicon layer having an oxide barrier layer. 
     
     
       6. The detector according to claim 5 in which said substrate includes an oxide layer on a p- wafer bonded to the oxide layer on said high resistivity epitaxial layer. 
     
     
       7. The detector according to claim 6 in which said substrate comprises an n+ wafer; said epitaxial high resistivity layer being formed on said n+ wafer. 
     
     
       8. The detector according to claim 7 in which said oxidized barrier layer comprises a first oxide layer formed on said high resistivity epitaxial layer, a second oxide layer formed on a p- wafer; said first and second oxide layers being placed together and bonded by an oxidation process. 
     
     
       9. The detector according to claim 8 in which said substrate has a nominal thickness in the range of 3,000 to 5,000 angstroms.